1. Field of the Invention
The present invention relates to an image sensor comprising a light receiving element.
2. Description of the Related Art
A light receiving element converts a light to an electric signal. For example, a light receiving element such as a CMOS or a CCD has a high sensitivity even in a range outside a visible light wavelength range (for example, a wavelength range of 400 nm to 700 nm) as the human visible range, in particular, it also has a high sensitivity in a wavelength range on the wavelength side longer than the visible light wavelength range (hereinafter, it is referred to as the “infrared range”). It is for example, a wavelength range of 700 nm to 1,200 nm).
An organic color filter used for extracting a specific color component from an incident light is disposed on the light incident side of the light receiving element. The light receiving element receives the incident light via the organic color filter. Since the color separation of the incident light is carried out by the organic color filter, the color component of an observation target is observed by the light receiving element.
However, since the organic color filter does not have an infrared ray cutting function, it is difficult to carry out the color separation in the infrared range.
In order to prevent the light observation in the infrared range, in some cases a reflection type infrared ray cutting filter comprising an inorganic multi layer film and an infrared ray absorbing type infrared ray cutting filter can be disposed on the light incident side of the light receiving element so as to be used in the optical system of a camera in combination.
FIG. 35 is a graph showing an example of the relationship between the wavelength and the transmittance of the reflection type infrared ray cutting filter and the absorbing type infrared ray cutting filter.
The reflection type infrared ray cutting filter is provided by forming the inorganic multi layer film on a glass plate.
According to the absorbing type infrared ray cutting filter, the infrared ray is absorbed by a dye or a copper ion. There are a plurality of kinds of the infrared ray absorbing type infrared ray cutting filters such as a type using a glass including a metal ion or a type using an organic dye system.
Although the reflection type infrared ray cutting filter comprising the inorganic multi layer film has a high infrared ray cutting function with respect to an incident light in the direction perpendicular to the filter surface, it is difficult to realize a sufficient cutting function with respect to an infrared ray with an angle such as the oblique incidence.
Therefore, for the purpose of compensating the cutting function of the reflection type infrared ray cutting filter comprising the inorganic multi layer film and reducing the influence of the oblique incidence or a re-incidence of the infrared ray, the infrared ray absorbing type infrared ray cutting filter is used in combination with the reflection type infrared ray cutting filter comprising the inorganic multi layer film.
Comparing the reflection type infrared ray cutting filter and the absorbing type infrared ray cutting filter, the absorbing type infrared ray cutting filter is more inexpensive than the reflection type infrared ray cutting filter. Moreover, as mentioned above, the absorbing type infrared ray cutting filter has a better infrared ray cutting performance of an incident light with an angle than that of the reflection type infrared ray cutting filter.
Therefore, in general, the absorbing type infrared ray cutting filter tends to be used more frequently than the reflection type infrared ray cutting filter.
As the conventional image sensor, there is a solid image sensor comprising a color purity compensating filter having a function of compensating the color purity by selectively cutting a light in a specific wavelength range at the border between a red light and a green light and/or the border between a green light and a blue light, and furthermore, having a function of cutting the infrared ray (for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-19322: hereinafter, it is referred to as the document 1).
Moreover, as the conventional image sensor, there is a color image sensor including an infrared ray absorbing agent for dramatically reducing the transmittance in an infrared ray range and transmitting a light in a visible light range for providing an infrared ray cutting ability, provided with a spectral filter in the front surface of the image sensor main body (for example, Jpn. Pat. Appln. KOKAI Publication No. 63-73204: hereinafter it is referred to as the document 2).
However, in the case of using the absorbing type infrared ray cutting filter, since the absorbing type infrared ray cutting filter has a thickness of about 1 to 3 mm, the miniaturization of a camera, or the like may be difficult.
Moreover, in the case of assembling the infrared ray cutting filter in a lens system as a camera part, a cost reduction may be difficult.
The image sensors of the above-mentioned documents 1, 2 comprise the infrared ray cutting filter for covering the entire front surface of the image sensor main body. Therefore, the infrared ray is cut with respect to the all light receiving elements included in the image sensor so that a difference may be generated between the observation by the light receiving elements and the human visual sensitivity.
For example, according to the document 2, as it is shown in FIGS. 2 and 10 of the document 2, the infrared ray cutting filter absorbs a light in the human visible light wavelength range of 550 nm to 700 nm. In the case where the infrared ray is cut with respect to all the light receiving elements included in the image sensor, the green sensitivity, and in particular, the red sensitivity may be deteriorated.